Scientists Detect Heme in 115-Million-Year-Old Dinosaur Bone, Setting Oldest Record for Blood Chemistry in Fossils

An international team led by chemists at Curtin University in Australia has reported something the field has long argued was chemically impossible: heme, the iron-containing molecule at the core of hemoglobin, detected inside microscopic structures interpreted as fossilized red blood cells in a 115-million-year-old dinosaur bone.

The paper, published November 2 in the Proceedings of the National Academy of Sciences, describes limb bones from Aratasaurus museunacionali, a small coelurosaurian theropod recovered from northeastern Brazil. The team combined microscopic imaging with spectroscopic chemical analysis to look for organic signatures inside ellipsoidal microstructures lodged within the bone's vascular canals.

What they found, according to the PNAS paper reviewed by ETL Newswire, was heme B and a chemically altered derivative called 3,8-diethyl heme B, localized within those same structures. That co-localization is the crux of the claim. Prior studies had reported morphological candidates for red blood cells in dinosaur fossils, and others had flagged organic molecules in ancient bone, but the team argues this is the first time heme has been detected in situ, directly inside the cellular structures themselves, in any dinosaur specimen.

The age matters as a benchmark. Previous reports of possible dinosaur blood cell structures reach back roughly 80 million years at most. At 115 million years, these Cretaceous bones extend that potential record by 35 million years or more.

The preservation mechanism deserves as much attention as the find itself. The researchers also detected hausmannite, a manganese oxide mineral, throughout the samples. According to reporting by Popular Science on the paper, this mineral appears to have helped stabilize the cellular architecture and additional biomolecules, including collagen-derived amino acids. The implied model is that geochemical mineralization, not simple organic survival, is what allowed heme-derived signals to persist. As one researcher put it in comments reviewed by ScienceAlert, the useful frame is "the original biological structure interacting with its surrounding geochemical environment" rather than a pristine cell sitting unchanged for over 100 million years.

That framing is exactly the right one to hold onto. The paper does not claim intact hemoglobin protein survived. It claims heme-derived tetrapyrroles, the porphyrin ring system that gives hemoglobin its oxygen-carrying capacity, left detectable chemical footprints. Those are very different claims with very different taphonomic plausibility.

Not every expert is persuaded. Live Science reported that the findings have drawn skepticism from outside researchers who aren't ready to accept the structures as confirmed red blood cells. The interpretive leap from "ellipsoidal microstructure in a vascular canal" to "fossilized red blood cell" requires ruling out microbial contamination, diagenetic artifacts, and other abiotic explanations. The methods section of the PNAS paper addresses contamination controls, but peer review did not close that debate, it opened a new round of it.

The study was led by Kliti Grice at Curtin University and received funding through a 2021 Australian Research Council Laureate Fellowship. The bones themselves come from the Museu Nacional collection in Brazil, and the species name, museunacionali, honors that institution, which lost much of its collection to a catastrophic fire in 2018.

If the heme identification holds up to independent replication, the implications run in two directions. For paleobiology, it would establish a new lower bound on how long blood-derived chemistry can survive in the fossil record under the right mineralogical conditions. For astrobiology, the team has noted, it raises the question of whether similar geochemical preservation pathways could protect biosignatures in extraterrestrial rock samples. That's a bigger claim, and one that will need its own evidence. For now, the PNAS paper stands as a detailed, chemically specific argument that the fossil record's molecular repertoire extends further back than the field generally assumed.

Sources cited:
- Proceedings of the National Academy of Sciences (PNAS) (https://www.pnas.org/doi/10.1073/pnas.2614248123)
- Sci.News (https://www.sci.news/paleontology/cretaceous-dinosaur-red-blood-cells-15169.html)
- Popular Science (https://www.popsci.com/science/first-dinosaur-blood-fossil-discovery/)
- ScienceAlert (https://www.sciencealert.com/dinosaur-blood-cells-detected-in-115-million-year-old-fossil)
- Live Science (https://www.livescience.com/animals/dinosaurs/traces-of-ancient-blood-found-in-115-million-year-old-dinosaur-fossil-new-study-claims)
- EurekAlert (https://www.eurekalert.org/news-releases/1149712)